A related-art power converter to be driven through PWM control computes a command voltage value from a command current value for a load and a detected current value, compares the command voltage value with a triangular wave carrier signal, and drives the power converter by producing a PWM pulse signal, thereby controlling the load. In this case, there is adopted a sample-and-hold method for simultaneously sampling the command value and the detected value and reading the thus-sampled values.
However, pulsating components (current ripples) present in a detected current value. For this reason, a power converter less susceptible to the influence of pulsating components is proposed in JP-A-9-154283.
In order to eliminate the pulsating components, the thus-proposed power converter is provided with a sampled value compensator for averaging an output from a sample-and-hold device for sampling a command value, thus eliminating a pulsating component.
However, such a power converter has a sampled-value compensator for eliminating pulsating components included in a detected current value. An average current value obtained by way of the sampled value compensator is to be controlled by the power converter. Even when an abrupt change has arisen in the detected current value, the sampled value compensator averages the change, thus impeding achievement of a sufficient high-speed response.
When an average produced by the sampled compensator is relaxed in order to achieve a high-speed response, current ripples stemming from PWM control is superimposed on a detected current value. In such a case, no current ripples are included in the command current value, and hence a voltage command value calculator produces a voltage to be used for reducing current ripples. As a result, variations in the command voltage value become greater. FIG. 19 shows that state, wherein a command voltage value varies greatly, and a triangular wave carrier signal and the command voltage value cross each other a plurality of times during a half cycle of a triangular wave carrier signal. Therefore, the number of pulses of the PWM signal output from a comparator increases in areas enclosed by circles in the drawing. The PWM signal is for driving a power switching element provided in the power converter. When an increase in the number of pulses arises, the number of times the power switching element is switched is also increased, thus increasing a switching loss. For this reason, there arises a problem of a necessity for adopting a power switching element having a large rated capacity.